ok, I have exactly the same problem. version 4.9.11 downloads at about 10 times slower than 4.8.1. (I tried it with the very same file/same sources)

my config:
Windows XP SP2
AMD 2800+
1024 MB RAM
Dial up connection
Java Version 1.5.3
Kerio Personal Firewall 4.2.0
NOD32 AV
and I consider myself as an experienced LimeWire user.
thnx in advance.